Method and apparatus for transmitting high bandwidth signals with low bandwidth transponders

ABSTRACT

A method and apparatus for transmitting a plurality of elementary data streams to a plurality of receivers is disclosed. In one embodiment, the method comprises the steps of generating M data streams comprising K multiplexed elementary data streams in a first entity, transmitting the M data streams to a second entity, generating N transmitter streams from the M data streams in the second entity; and transmitting each of the N transmitter streams to the plurality of receivers using an associated one of N broadcast sub-transmitters.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/829,916, entitled “METHOD AND APPARATUS FOR TRANSMITTING HIGHBANDWIDTH SIGNALS WITH LOW BANDWIDTH TRANSPONDERS,” by Romulo Pontual etal., filed Mar. 14, 2013, which application is a continuation-in-part(CIP) of U.S. patent application Ser. No. 13/484,756, entitled“COMBINING TRANSPONDER BANDWIDTHS FOR SOURCE AND FEC ENCODINGEFFICIENCY,” by Ernest Chen, filed May 31, 2012, which is a continuationof U.S. application Ser. No. 11/193,856, entitled “COMBINING TRANSPONDERBANDWIDTHS FOR SOURCE AND FEC ENCODING EFFICIENCY,” by Ernest Chen,filed Jul. 29, 2005, now issued as U.S. Pat. No. 8,200,149, issued Jun.12, 2012, all of which applications are hereby incorporated by referenceherein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to systems and methods for the spectralefficient transmission of signals, and more particularly, for combiningtransponder bandwidths for source and forward error correction encodingefficiency.

2. Description of the Related Art

Digital Direct Broadcast Systems (DBS), such as DIRECTV®, which isprovided by the assignee of the present invention, have become verysuccessful. However, as such systems evolve, there is an increasingdemand for additional bandwidth and/or more efficient use of existingbandwidth to carry an ever-increasing set of audio, video and dataservices.

Transmission of video signals over fixed capacity transmission channelsposes a number of technical challenges. Raw, uncompressed video requiresbandwidth that can exceed the available bandwidth on a satellite channelby orders of magnitude. Video is therefore compressed prior totransmission, using techniques based on standards such as MPEG-2 andMPEG-4|H.264. These techniques can greatly reduce the required bandwidthwhile maintaining high visual quality. They do result, however, in acompressed bit stream that has a variable bit-rate. This is because theamount of compression achieved greatly depends on the actual content ofthe video: scenes with complicated texture or fast moving objects arecompressed less and vice versa.

Typical wireless transmission channels, on the other hand, have a fixedtransmission rate. To accommodate a variable bit-rate compressed videosignal, the fixed wireless channel rate must exceed the peak bit-rate ofthe video signal. If the peak bit-rate of a compressed video signalexceeds its average bit-rate by a significant amount (usually the casewith most types of content) there is a significant waste of the wirelesschannel capacity. This is typically a precious resource, especially whenthe wireless transmissions are made via satellite. For example, if theaverage video bit-rate is 10 mbps and its peak bit-rate is 25 mbps, itwould require a satellite channel with a capacity of at least 25 mbps,but on average, 15 mbps of capacity will be wasted.

To reduce this waste of transmission channel capacity, multiplecompressed video signals are usually multiplexed together using astatistical multiplexer (statmux) prior to transmission over the fixedbit-rate satellite channel. Since the peaks in the bit rate of one mediaprogram signal are unlikely to occur at the same time as the peaks inthe bit rate of a signal for another media program, the proportion ofthe channel capacity needed to account for bit rate variance is reduced.This allows the bit rate of the combined signal to be more closelymatched to the channel capacity, thus reducing waste of transmissioncapacity.

According to the central limit theorem , the variance of the sum of Nrandom variables is the sum of the variance of each random variable.Hence, as N increases to include more random variables, the variabilityof the sum of those random variables decreases. Considering theinstantaneous bit rate of a video stream to be a random variable with avariance and a mean, one would expect the variance of the instantaneousbit rate of N video streams to be a smaller proportion of the averagebit rate as the number of video streams goes up.

For example, suppose a signal comprises the sum of five signals, eachhaving an instantaneous bit rate with an average of 10 mbps and astandard deviation of 5 mbps (hence, a variance of 25 mbps). Since thereare five such signals, the average bit rate for the combined fivesignals will be 50 mbps, and the variance of the combined five signalswill be 5*25=125 mbps, which equates a standard deviation of about 11.2mbps. As can be seen from this example, although the averageinstantaneous bit rate quintupled, the standard deviation of thatinstantaneous bit rate increased by only a little more than a factor oftwo. Since the channel capacity must accommodate the peak bit rate,combining five such signals reduces the overhead required because thevariance of the combined signal is reduced. This is because while onesignal may have an instantaneous bit rate well above its average,another signal may have an instantaneous bit rate well below itsaverage, thus allowing transmission of both signals with little or nooverhead.

For an even simpler example, consider a signal with five video signalshaving the above characteristics (10 mbps average bit-rate and a peakbit rate of 25 mbps). If those signals are multiplexed such that the 25mbps peak bit rate in one signal can be combined with 5 mbps bit ratetroughs in two signals and 10 mbps average rate of the other twosignals, the total bit rate capacity requirement is 55 mbps (5*10 mbpsaverage rate plus [15−(2*5)] to account for the peaks), which is only 15mbps (or 30%) more than the sum of the five average bitrates (50 mbps).

In practice, additional bandwidth is required for audio, errorcorrection and transport signaling overhead, but the foregoing simpleexamples illustrate how statistical multiplexing can reduce the wasteassociated with transmitting a variable bit-rate compressed video signalover a fixed bit-rate channel such as that of a satellite transponder.This reduced waste can be used to increase channel capacity.

If the capacity of the fixed bit-rate channel is not significantlygreater than the average bit-rate of the compressed signals (say atleast four or five times), then little will be gained by statisticalmultiplexing. With the advent of high-bit rate content such as 4KTV,full resolution 3DTV and even 1080p60 content, existing satellitetransponders will not have the capacity of transmitting several suchstreams, even if they are statistically multiplexed together. There istherefore the need to find a solution to maintain the gains ofstatistically multiplexing several such high bit-rate compressed videosignals while at the same time using the existing satellite transmissioncapabilities.

SUMMARY OF THE INVENTION

To address the requirements described above, a method and apparatus fortransmitting a plurality of elementary data streams to a plurality ofreceivers is disclosed herein. In one embodiment, the method comprisesthe steps of generating M data streams comprising K multiplexedelementary data streams in a first entity, transmitting the M datastreams to a second entity, generating N transmitter streams from the Mdata streams in the second entity; and transmitting each of the Ntransmitter streams to the plurality of receivers using an associatedone of N broadcast sub-transmitters. In another embodiment, theapparatus comprises a signal distributor, for generating M data streamscomprising K multiplexed elementary data streams, and a broadcasttransmitter, having N broadcast sub-transmitters. The broadcasttransmitter wirelessly receives the M data streams from the signaldistributor, generates N broadcast sub-transmitter data streams from thereceived M data streams, and transmits the N broadcast sub-transmitterdata streams via an associated one of the N broadcast sub-transmittersto the plurality of receivers.

Hence, N broadcast sub-transmitters can be used to transmit K multiplevideo signals that have been statistically multiplexed together anduplinked as M data streams. The statistically multiplexed video signalsconstitute a ‘fat pipe’ that is then split up and transmitted overmultiple ‘bonded’ transponders in a manner that allows reconstitution ofthe fat pipe at the receiver without loss of data and without increasedlatency.

BRIEF DESCRIPTION OF THE DRAWINGS

Referring now to the drawings in which like reference numbers representcorresponding parts throughout:

FIG. 1 is a diagram illustrating an exemplary direct broadcast satellitesystem according to a preferred embodiment of the present invention;

FIG. 2 is a block diagram showing a typical uplink configuration for asingle transponder, showing how video program material is uplinked bythe control center and the uplink center;

FIG. 3A is a diagram of a representative data stream;

FIG. 3B is a diagram of a data packet;

FIG. 4 is a block diagram that further illustrates an exemplary signaltransmission system according to the preferred embodiment of the presentinvention;

FIG. 5 is a block diagram that further illustrates an exemplary signalreception system according to the preferred embodiment of the presentinvention;

FIG. 6 is a block diagram of showing additional details of an exemplaryreceiver;

FIG. 7 illustrates the insertion of guard-band signals between legacyband signals according to the preferred embodiment of the presentinvention; and

FIG. 8 illustrates the construction of high spectral-efficiency signalsaccording to the preferred embodiment of the present invention;

FIG. 9 is a diagram illustrating exemplary method steps that can be usedto transmit media programs and other data using a generalizedtransmission system in which the number of uplink data streams M neednot be equal to the number of downlink transmitter streams N;

FIG. 10 is a diagram illustrating an exemplary embodiment of thegeneralized transmission system;

FIG. 11 is a diagram illustrating another embodiment of the generalizedtransmission system, in which the M data streams are transmitted to twobroadcast transmitter elements; and

FIG. 12 is a diagram illustrating an exemplary computer system 100 thatcould be used to implement elements of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description of the preferred embodiment, reference ismade to the accompanying drawings which form a part hereof, and in whichis shown by way of illustration a specific embodiment in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized and structural changes may be made withoutdeparting from the scope of the present invention.

Overview

The present invention combines transponder bandwidths using a wide-band“virtual” transponder comprising a plurality of narrow-band physicaltransponders for transmitting a single data stream. A plurality ofelementary streams are statistically multiplexed to create the singledata stream. The single data stream is forward error correction encodedfor channel impairment correction. The single encoded data stream isdemultiplexed into a plurality of transponder streams, and eachtransponder stream is modulated and transmitted to the receivers. Uponreceipt from the plurality of narrow-band physical transponders, thetransponder streams are demodulated and multiplexed to recover thesingle data stream. The recovered single data stream is forward errorcorrection decoded and demultiplexed to recover the plurality ofelementary streams.

This technique allows for the efficient use of a signal spectrumrepresented by the transmissions from each transponder. For example, thephysical transponders may each use a different portion of a signalspectrum that is non-contiguous with other portions of the signalspectrum. This signal spectrum may include spectrum that was once usedfor guard bands. Coding latency is also reduced. The time duration of aforward error correction (FEC) code for a single signal is quite longdue to the small symbol rate offered by the single signal. By “pooling”the bandwidths of multiple narrow-band signals (e.g. multiple mediaprograms) for the FEC code, the effective symbol rate is increased,resulting in a significant reduction in code length and therefore codelatency. This can be important since more powerful and longer turbocodes are increasingly used in quasi-error free communication.

Transmission System

FIG. 1 is a diagram illustrating an exemplary transmission system 100according to one embodiment of the present invention. In the illustratedembodiment, includes a signal distributor 101, a broadcast transmitter118, and a plurality of receiving stations 108. The signal distributor101 may comprises a control center 102 operated by a service provider incommunication with an uplink center 104 via a link 106, and thereceiving stations 108 may communicate with the control center 102 via alink 110. The control center 102 provides broadcast materials to theuplink center 104 and coordinates with the receiving stations 108 tooffer various services, including key management for encryption anddecryption, etc.

The uplink center 104 receives the broadcast materials from the controlcenter 102 and, using an antenna 112 and uplink transmitter 222,transmits the broadcast materials via uplink 116 to the broadcasttransmitter 118, which may include one or more broadcast transmitterelements 119A-119D such as satellites and/or terrestrial transmitters,each of which may include one or more broadcast sub-transmitters ortransponders 120. The broadcast transmitters 118 receive and process thebroadcast materials, and re-transmit the broadcast materials toreceiving stations 108 via a downlink 122 using thetransmitters/transponders 120. Receiving stations 108 receive thebroadcast materials from the broadcast transmitters 118 via an antenna124, and decrypt and decode the broadcast materials using a receiver126.

Uplink Configuration

FIG. 2 is a block diagram showing a typical uplink configuration for asingle transponder, showing how video program material is uplinked bythe control center 102 and the uplink center 104. FIG. 2 shows threevideo channels (which could be augmented respectively with one or moreaudio channels for high fidelity music, soundtrack information, or asecondary audio program for transmitting foreign languages), and a datachannel from a program guide subsystem 206 and data such as softwareupdates from a data source 208.

The video channels are provided by a program source of video material200A-200C (collectively referred to hereinafter as video source(s) 200).The data from each video program source 200 is provided to ancompression encoder 202A-202C (collectively referred to hereinafter asencoder(s) 202). Each of the encoders 202 accepts a program time stamp(PTS) from the controller 216. The PTS is a wrap-around binary timestamp that is used to assure that the video information is properlysynchronized with the audio information after encoding and decoding. APTS time stamp is sent with each I-frame of the MPEG encoded data.

In one embodiment of the present invention, each encoder 202 is a secondgeneration Motion Picture Experts Group (MPEG-2) encoder, but otherencoders implementing other coding techniques can be used as well. Thedata channel can be subjected to a similar compression scheme by anencoder (not shown), but such compression is usually either unnecessary,or performed by computer programs in the computer data source (forexample, photographic data is typically compressed into *.TIF files or*JPG files before transmission). After encoding by the encoders 202, thesignals are converted into data packets by a packetizer 204A-204F(collectively referred to hereinafter as packetizer(s) 204) associatedwith each source 200.

The data packets are assembled using a reference from the system clock214 such as a program clock reference (PCR), and from the conditionalaccess manager 210, which provides the SCID to the packetizers 204 foruse in generating the data packets. These data packets are thenmultiplexed by multiplexer 205 into serial data and transmitted. Theserial data may be further forward error correction encoded by FECencoder 218 before transmitted by one or more transmitters 222 havingone or more modulators 220 and one or more antennas 112.

Broadcast Data Stream Format and Protocol

FIG. 3A is a diagram of a representative data stream. The first packetsegment 302 comprises information from video channel 1 (data comingfrom, for example, the first video program source 200A). The next packetsegment 304 comprises computer data information that was obtained, forexample from the computer data source 208. The next packet segment 306comprises information from video channel 5 (from one of the videoprogram sources 200). The next packet segment 308 comprises programguide information such as the information provided by the program guidesubsystem 206. As shown in FIG. 3A, null packets 310 created by the nullpacket module 212 may be inserted into the data stream as desired.

The data stream therefore comprises a series of packets from any one ofthe data sources in an order determined by the controller 216. The datastream is encrypted by the encryption module 218, modulated by themodulator 220 (typically using a QPSK modulation scheme), and providedto the transmitter 222, which broadcasts the modulated data stream on afrequency bandwidth to the satellite via the antenna 106. The receiver126 receives these signals, and using the SCID, reassembles the packetsto regenerate the program material for each of the channels.

FIG. 3B is a diagram of one embodiment of a data packet. Each datapacket (e.g. 302-316) is 147 bytes long, and comprises a number ofpacket segments. The first packet segment 320 comprises two bytes ofinformation containing the SCID and flags. The SCID is a unique 12-bitnumber that uniquely identifies the data packet's data channel. Theflags include 4 bits that are used to control whether the packet isencrypted, and what key must be used to decrypt the packet. The secondpacket segment 322 is made up of a 4-bit packet type indicator and a4-bit continuity counter. The packet type identifies the packet as oneof the four data types (video, audio, data, or null). When combined withthe SCID, the packet type determines how the data packet will be used.The continuity counter increments once for each packet type and SCID.The next packet segment 324 comprises 127 bytes of payload data, whichis a portion of the video program provided by the video program source300 or other audio or data sources. The final packet segment 326 is datarequired to perform forward error correction.

Other data packetization protocols may be used, including protocols usedin DVB/DVBS2 or the protocol described in the MPEG-2 TransportSpecification as described in ISO/IEC 13818-1 “Systems,” 2000, which ishereby incorporated by reference herein.

Signal Transmission

FIG. 4 is a block diagram that illustrates further features of anexemplary signal transmission system according to a bent-pipe embodimentof the present invention. In this embodiment, the transmitters 120comprise transponders that transpond (receive and retransmit) the uplinksignal as a downlink signal, with minimal, if any processing exceptfrequency translation.

The control center 102 includes a plurality (K) of video and/or audioencoders 202 that each encode a video and/or audio source into a videoelementary stream (VES) and/or audio elementary stream (AES) 201. Theresulting K video and/or audio elementary streams 203 are statisticallymultiplexed by statistical multiplexer 205, wherein the value K:1indicates a multiplexing ratio that matches the throughput of thesystem.

The resulting single data stream may be optionally FEC encoded at by FECencoder 218. After encoding, the single encoded data stream isdemultiplexed by demultiplexer 408 into N transponder data streams,wherein the value 1:N indicates a demultiplexing ratio that matches thenumber of transponders 120 being used.

In the uplink center 104, each of the N transponder data streams isseparately modulated by the uplink transmitter 222 having a plurality ofmodulators 220, and then uplinked via antenna 112 to one or moresatellites 118. A plurality N of the transponders 120 on the satellites118 (where N may comprise all of the transponders 120 or a subset of thetransponders 120) are treated as a “virtual” transponder 412, whereineach of the N transponder data streams is routed to a different one ofthe N transponders 120 for re-transmission. Note that all N transponders120 do not have to be of the same bandwidth, and together they may carrya combination of legacy and guard-band signals as may be desired. In oneembodiment, the number of transponders N used to transmit the Kmultiplexed elementary data streams is determined such that although thebit rate of the single stream from the multiplexer 205 may exceed thebit rate of any one of the N physical transponders, it does not exceedthe combined bit rate of the N physical transponders. For example, ifeach of the K multiplexed elementary data streams has an associatedtemporally varying peak bit rate of BRD₁(t), BRD₂(t), . . . ,BRD_(K)(t), the single intermediate data stream will have a peak bitrate of:

${{BRS}(t)} \geq {\sum\limits_{i = 1}^{K}\; {{{BRD}_{i}(t)}.}}$

Note that the single intermediate data stream will have a bit rate atleast equal to the sum of the bit rates of the elementary data streams,and might be greater because of the addition of null packets. However,since it is unlikely that the peak bit rates of each elementary streamwill temporally coincide, the single intermediate data stream willordinarily have a peak bit rate of less than the sum of the peak bitrates for each of the K elementary data streams. This reduction is knownas the statmux gain.

Further, if each of the N physical transmitters has an associatedmaximum bit transmission rate of BRT₁, BRT₂, . . . , BRT_(N), the numberof transponders N to transmit the K elementary streams can be selectedsuch that

${\sum\limits_{i = 1}^{N - 1}\; {BRD}_{i}} < {{BRS}(t)} \leq {\sum\limits_{i = 1}^{N}\; {BRT}_{i}}$

for all time t. In cases where the N transponders 120 have differentmaximum bit transmission rates, the sum of the maximum bit transmissionrates for the transponders 120 selected for use must exceed the bit rateof the single intermediate data stream.

Signal Reception

FIG. 5 is a block diagram that further illustrates an exemplary signalreception system according to the preferred embodiment of the presentinvention. As in FIG. 4, a plurality N of the transponders 120 on thebroadcast transmitter 118 (where N may comprise all of the transponders120 or a subset of the transponders 120) are treated as a “virtual”transponder 412, wherein each of the N transponder data streams isrouted to a different one of the N transponders 120 for re-transmission.At the receiving stations 108, each of the N transponder data streams isdownlinked from the broadcast transmitter 118 via antenna 124 andreceiver 126. In the receiver 126, each of the N transponder datastreams is separately demodulated using demodulators 500. Afterdemodulation, the N transponder data streams are properly time-alignedand multiplexed by multiplexer 502 to recover the single encoded datastream.

This time alignment can be performed using time reference informationsuch as the PTS described above, or equivalent time stamps found in anMPEG data stream such as the reference time stamp or program time stamp.For example, the received data can be temporarily stored and retrieved,and sorted before presentation according to the time referenceinformation.

The single encoded data stream is then optionally FEC decoded by decoder504. The resulting single data stream is demultiplexed by demultiplexer506 to recover the K plurality of video and/or audio elementary streams508. Each of the K video and/or audio elementary stream 508 are decodedby one of a plurality K of video and/or audio decoders 510 to completethe signal reception.

The foregoing illustrates an embodiment in which a the K data streams201 are multiplexed together into a single data stream, and encoding isperformed on that single data stream. Further, the signals from eachtransponder are multiplexed together into a single data stream that isFEC decoded before demultiplexing the stream to recover the K datastreams 508. As described herein this increases the efficiency of theFEC encoding and decoding processes, as it provides a longer stream tothe FEC encoder 218 and decoder 504.

Alternatively, the FEC encoding can be performed separately on eachportion of the data stream after demultiplexing by demultiplexer 408,for example by using an FEC encoder incorporated into each of themodulators 220 and a decoder incorporated into each demodulator 500.

Set Top Box

FIG. 6 is a block diagram showing additional details of an exemplaryreceiver 126. The receiver 126 comprises one or moretuner/demodulator(s) 500A-500N communicatively coupled to an outdoorunit (ODU) coupled to antenna 124 having one or more Low Noise Block(LNB) downconverters 602. The LNB 602 converts downlink 118 signal fromthe broadcast resource 118 to a signal required by the receiver's 126tuner/demodulators 500A-500N. The LNB 602 may provide either a dual or asingle output. The single-output LNB 602 has only one RF connector,while a multiple output LNB 602 has multiple RF output connectors andcan be used to feed a another tuner/demodulator 500, a second receiver126 or some other form of distribution system.

Each tuner/demodulator 500 isolates a single broadcastsub-transmitter/transponder 120, and converts the modulated data to adigital data stream. As packets are received, each tuner/demodulator 500identifies the type of each packet. If the tuner/demodulator 500identifies a packet as program guide data, the tuner/demodulator 500outputs the packet to memory. The digital data streams are then providedto multiplexer 502 and then to a forward error correction (FEC) decoder505. This allows the receiver 126 to reassemble the data transmitted bythe uplink center 104 (which applied the forward error correction to thedesired signal before transmission to the subscriber receiving station110) verifying that the correct data signal was received and correctingerrors, if any. The error-corrected data may be fed from the FEC decodermodule 606 to the transport module 608 via an 8-bit parallel interface.

The transport module 608 performs many of the data processing functionsperformed by the receiver 126. The transport module 608 processes datareceived from the FEC decoder module 606 and provides the processed datato the video MPEG decoder 614, the audio MPEG decoder 616, and themicrocontroller 610 and/or data storage processor 630 for further datamanipulation. In one embodiment of the present invention, the transportmodule, video MPEG decoder and audio MPEG decoder are all implemented onintegrated circuits. This design promotes both space and powerefficiency, and increases the security of the functions performed withinthe transport module 608. The transport module 608 may also perform theoperations 1:K demultiplexing operations described above, or thoseoperations may be performed external to the transport module 608.

The transport module 608 also provides a passage for communicationsbetween the microprocessor 610 and the video and audio MPEG decoders614, 616. As set forth more fully hereinafter, the transport module alsoworks with the conditional access module (CAM) 612 to determine whetherthe subscriber receiving station 110 is permitted to access certainprogram material. Data from the transport module can also be supplied toexternal communication module 626.

The CAM 612 functions in association with other elements to decode anencrypted signal from the transport module 608. The CAM 612 may also beused for tracking and billing these services. In one embodiment of thepresent invention, the CAM 612 is a smart card, having contactscooperatively interacting with contacts in the receiver 126 to passinformation. In order to implement the processing performed in the CAM612, the receiver 126, and specifically the transport module 608provides a clock signal to the CAM 612.

Video data is processed by the MPEG video decoder 614. Using the videorandom access memory (RAM) 636, the MPEG video decoder 614 decodes thecompressed video data and sends it to an encoder or video processor 615,which converts the digital video information received from the videoMPEG module 614 into an output signal usable by a display or otheroutput device. By way of example, processor 615 may comprise a NationalTV Standards Committee (NTSC) or Advanced Television Systems Committee(ATSC) encoder. In one embodiment of the invention both S-Video,baseband video and RF modulated video (NTSC or ATSC) signals areprovided. Other outputs may also be utilized, and are advantageous ifATSC high definition programming is processed.

Audio data is likewise decoded by the MPEG audio decoder 616. Thedecoded audio data may then be sent to a digital to analog (D/A)converter 618. In one embodiment of the present invention, the D/Aconverter 618 is a dual D/A converter, one for the right and leftchannels. If desired, additional channels can be added for use insurround sound processing or secondary audio programs (SAPS). In oneembodiment of the invention, the dual D/A converter 618 itself separatesthe left and right channel information, as well as any additionalchannel information. Other audio formats such as DOLBY DIGITAL AC-3 maysimilarly be supported.

A description of the processes performed in the encoding and decoding ofvideo streams, particularly with respect to MPEG and JPEGencoding/decoding, can be found in Chapter 8 of “Digital TelevisionFundamentals,” by Michael Robin and Michel Poulin, McGraw-Hill, 1998,which is hereby incorporated by reference herein.

The microprocessor 610 receives and processes command signals from theremote control 624, a receiver keyboard interface, modem 640, andtransport 608. The microcontroller receives commands for performing itsoperations from a processor programming memory, which permanently storessuch instructions for performing such commands. The memory used to storedata for microprocessor 610 and/or transport 608 operations may comprisea read only memory (ROM) 638, an electrically erasable programmable readonly memory (EEPROM) 622, a flash memory 652 and/or a random accessmemory 650, and/or similar memory devices. The microprocessor 610 alsocontrols the other digital devices of the receiver 126 via address anddata lines (denoted “A” and “D” respectively, in FIG. 6).

The modem 640 connects to the customer's phone line via the PSTN port120. It calls, e.g. the program provider, and transmits the customer'spurchase information for billing purposes, and/or other information. Themodem 640 is controlled by the microprocessor 610. The modem 640 canoutput data to other I/O port types including standard parallel andserial computer I/O ports. Data can also be obtained from a cable ordigital subscriber line (DSL) modem, or any other suitable source.

The receiver 126 may also comprise a local storage unit such as thestorage device 632 for storing video and/or audio and/or other dataobtained from the transport module 608. Video storage device 632 can bea hard disk drive, a read/writeable compact disc of DVD, a solid stateRAM, or any other storage medium. In one embodiment of the presentinvention, the video storage device 632 is a hard disk drive withspecialized parallel read/write capability so that data may be read fromthe video storage device 632 and written to the device 632 at the sametime. To accomplish this feat, additional buffer memory accessible bythe video storage 632 or its controller may be used. Optionally, a videostorage processor 630 can be used to manage the storage and retrieval ofthe video, audio, and/or other data from the storage device 632. Thevideo storage processor 630 may also comprise memory for buffering datapassing into and out of the video storage device 632. Alternatively orin combination with the foregoing, a plurality of video storage devices632 can be used. Also alternatively or in combination with theforegoing, the microprocessor 610 can also perform the operationsrequired to store and or retrieve video and other data in the videostorage device 632.

The video processing module 615 output can be directly supplied as avideo output to a viewing device such as a video or computer monitor. Inaddition the video and/or audio outputs can be supplied to an RFmodulator 634 to produce an RF output and/or 8 vestigial side band (VSB)suitable as an input signal to a conventional television tuner. Thisallows the receiver 126 to operate with televisions without a videoinput.

Each of the broadcast resource elements 119 comprises one or moretransponders, each of which accepts program information from the uplinkcenter 104, and relays this information to the subscriber receivingstation 110. Known multiplexing techniques are used so that multiplechannels can be provided to the user. These multiplexing techniquesinclude, by way of example, various statistical or other time domainmultiplexing techniques and polarization multiplexing. In one embodimentof the invention, a single transponder operating at a single frequencyband carries a plurality of channels, each identified by respectiveservice channel identification (SCID).

Preferably, the receiver 126 also receives and stores a program guide ina memory available to the microprocessor 610. Typically, the programguide is received in one or more data packets in the data stream fromthe broadcast resource 118. The program guide can be accessed andsearched by the execution of suitable operation steps implemented by themicrocontroller 610 and stored in the processor ROM 638. The programguide may include data to map viewer channel numbers to satellitenetworks, satellite transponders and service channel identifications(SCIDs), and also provide TV program listing information to thesubscriber identifying program events.

Initially, as data enters the receiver 126, the tuner/demodulator 500looks for a boot object. Boot objects are always transmitted with thesame SCID number, so tuner 500 knows that it must look for packetsmarked with that identification number. A boot object identifies theidentification numbers where all other objects can be found.

As data is received and stored in the memory, the microprocessor 610acts as a control device and performs various operations on the data inpreparation for processing the received data. These operations includepacket assembly, object assembly and object processing.

The first operation performed on data objects stored in the memory 650is packet assembly. During the packet assembly operation, microprocessor610 examines the stored data and determines the locations of the packetboundaries.

The next step performed by microprocessor 610 is object assembly. Duringthe object assembly step, microprocessor 610 combines packets to createobject frames, and then combines the object frames to create objects.Microprocessor 610 examines the checksum transmitted within each objectframe, and verifies whether the frame data was accurately received. Ifthe object frame was not accurately received, it is discarded frommemory 650. Also during the object assembly step, the microprocessor 610discards assembled objects that are of an object type that themicroprocessor 610 does not recognize. The receiver 126 maintains a listof known object types in memory 650. The microprocessor 610 examines theobject header of each received object to determine the object type, andthe microprocessor 610 compares the object type of each received objectto the list of known object types stored in memory 650. If the objecttype of an object is not found in the list of known object types, theobject is discarded from memory 650. Similarly, the receiver 126maintains a list of known descriptor types in memory 650, and discardsany received descriptors that are of a type not in the list of knowndescriptor types.

The last step performed by microprocessor 610 on received object data isobject processing. During object processing, the objects stored in thememory 650 are combined to create a digital image. Instructions withinthe objects direct microprocessor 610 to incorporate other objects orcreate accessible user-links. Some or all of the digital images can belater converted to an analog signal that is sent by the receiver 126 toa television or other display device for display to a user.

The functionality implemented in the receiver 126 depicted in FIG. 6 canbe implemented by one or more hardware modules, one or more softwaremodules defining instructions performed by a processor, or a combinationof both.

Spectrum Examples

There are a number of advantages to the present invention. One advantageis that the present invention allows efficient use of a fragmentedsignal spectrum, such as from non-contiguous guard bands. Consider theexample shown in FIG. 7, which illustrates the insertion of guard bandsignals 700 between legacy band signals 702. In this example, the rateratio between the legacy band 702 and the guard band 700 isapproximately 4:1. To use these guard bands 700, the N transponder datastreams described in FIGS. 2 and 3 are transmitted by the N transponders120 in N guard bands. Alternatively, the N transponder data streamsdescribed in FIGS. 2 and 3 are transmitted by the N transponders 120 ina combination of N legacy bands and guard bands.

Another advantage is that the present invention allows narrow-bandtransponders 120 to simultaneously achieve high CNR andstatistical-multiplexing efficiencies. Consider the example shown inFIG. 8, which illustrates the construction of high spectral-efficiencysignals 800 in the legacy band 802. For high-throughput communication,spectral efficiency dictates a CNR that may be beyond current satelliteTWTA power availability. For a given TWTA power, reducing the signalbandwidth can increase the CNR enough to meet the requirement. Multipletransponders 120, properly configured and spaced in the frequency domainin this way, can cover the entire signal bandwidth of interest. Whileeach narrow-bandwidth signal might not support goodstatistical-multiplexing efficiency, the combined signal may do so withthe present invention.

Yet another advantage is that the present invention reduces FEC codelatency. The combined bandwidth provided by the present inventionincreases the effective symbol rate, thereby resulting in a shortenedtime duration of a given FEC.

Other Considerations

The communications system described herein is assumed to operate with aconstant-envelope signal on all transponders 120. Typically, asingle-carrier QPSK or 8PSK signal is used to maximize TWTA powerefficiency. Either single-channel or multiple-channel receivers 126 maybe used with the present invention.

In a single-channel receiver 126 design, a single tuner with a fast,single-set, analog-to-digital (A/D) converter covers several transponder120 signals that comprise a part or all of the virtual transponder 412.For example, if two guard bands 700 on either side of a legacy signalband 702 in FIG. 7 are to be combined, then the A/D converter of thereceiver 126 must cover the bandwidth depicted in FIG. 7. After A/Dconversion, digital filtering in the receiver 126 would be used toselect the two guard bands 700, demodulating the signals to extractrelevant information for further processing.

Alternatively, a multiple channel receiver 126 design may include atuner and A/D converter for each physical transponder 120. Compared witha single-tuner receiver 126, the tuners and A/Ds in this embodiment arereplicated in the receiver 126, but the A/Ds can be slower, as they onlyneed to cover a narrow-band signal from one of the transponders 120.

Additional Embodiments

In the above description, it is assumed that the bit-rates, bandwidth,or channel capacity of the uplink and downlink signals 116 and 122 arethe same. In this case, the satellite 118 transponders 120 simplyreceive and retransmit (possibly with frequency shifting) the uplinksignals 116. Hence, the broadcast transmitter 118 can be modeled asessentially a plurality of remote transponders. However, the uplink anddownlink bandwidths need not be identical. A more generalizedtransmission system 100 may utilize M uplink signals 116 and N downlinksignals 122.

For example, a single uplink signal 116 may be able to accommodate anentire multiplexed stream (M=1), but a single downlink signal 122 maynot be able to accommodate the entre stream, thus requiring a pluralityof downlink signals 122 (N?2). Similarly, multiple uplink signals 116may be required (M?1), but a single downlink signal 122 (N=1) may beable to accommodate the entire multiplexed stream.

FIG. 9 is a diagram illustrating exemplary method steps that can be usedto transmit media programs and other data using a generalizedtransmission system in which the number of uplink data streams M neednot be equal to the number of downlink transmitter streams N. FIG. 10 isa diagram illustrating an exemplary embodiment of the generalizedtransmission system 1000.

Turning first to FIG. 9, M data streams 1002A-1002M that comprise Kmultiplexed elementary data streams are generated, as shown in block902. This can be performed, for example, by the signal distributor 101,which may perform the functions described with respect to the controlcenter 102 and the uplink center 104 described above in connection withthe bent-pipe transmission system 100. As shown in FIG. 10, this may beaccomplished by statistically multiplexing the K elementary data streamswith a statistical multiplexer 205 to generate a single intermediatedata stream, then demultiplexing the single intermediate data streaminto M data streams 1010 using demultiplexer 408. The intermediate datastream may also be optionally coded (for example, error correctioncoded) by encoder 218 before application to the demultiplexer 408.

Returning again to FIG. 9, the M data streams 1002A-1002M aretransmitted to a broadcast transmitter 118, which may comprise one ormore of the satellites or terrestrial transmitters shown in FIG. 1. Thisis illustrated in block 904. This can be accomplished by uplinktransmitter 222 separately modulating each of the M data streams or by Mseparate uplink sub-transmitters 1004A-1004M as shown in FIG. 10.

The broadcast transmitter 118 receives the M data streams and generatesN transmitter streams 1012A-1012N from the received M data streams, asshown in block 906. In the illustrated embodiment, this is accomplishedby providing each of the received M modulated data streams to a receiver1006A-1006M associated with each of the M data streams (or one of aplurality of demodulators in a single receiver), and applying those Mdata streams to a recombiner or multiplexer 1008 to produce a recombineddata stream. The recombined data stream is then split or demultiplexedinto N data streams using splitter or demultiplexer 1010 to produce theN transmitter streams 1012A-1012N. The functions of the multiplexer 1008and demultiplexer 1010 may be combined into a single device whichperforms the transformation of M data streams to N data streams.

The N transmitter streams 1012A-1012N are then transmitted to one ormore of the receiver station(s) 108 with each of the N transmitterstreams being transmitted by an associated one of N physical broadcastsub-transmitters 1014A-1014N. In one embodiment, each of the Ntransmitter streams is associated with only one of the N physicalbroadcast sub-transmitters 1014A-1014N.

The N transmitter streams 1012A-1012N are received at the receiverstation 108, multiplexed to form a single stream, and the single streamis demultiplexed to recover the K elementary data streams, as shown inblocks 910-914. In one embodiment, this is accomplished by receiving thesignals from the N physical transmitters 1014A-1014N using a receiver1016A-1016N associated with one of the N transmitter streams1012A-1012N, or a single receiver having a plurality of demodulators,each associated with one of the N transmitter streams 1012A-1012N, andapplying the received N transmitter streams 1012A-1012N to a multiplexer502 to generate a single data stream. That single data stream mayoptionally be decoded (for example, FEC decoded) by decoder 504 beforebeing applied to multiplexer 506. The multiplexer 506 recovers one ormore of the K elementary data streams.

In one embodiment of the generalized transmission system 1000, thenumber of uplink data streams is the same as the number of downlink datastreams (M=N). In this embodiment, the broadcast transmitter 118 mayoperate analogously to the bent-pipe system 100 shown in FIG. 1, whereinthe K elementary data streams are formed into 5 transponder streams thatare transmitted to a broadcast transmitter 118. In this case, thebroadcast transmitter 118 does not require the splitter 1008 orrecombiner 1010, and the transmitters 1014A-1014N may comprise simpletransponders.

In another embodiment of the invention, the K elementary data streamscan be multiplexed into a single data stream that is transmitted to thebroadcast transmitter 118 using a single uplink signal 116 (M=1). Inthis embodiment, the demultiplexer 408 is not required and only one ofthe transmitters 1004 are required to uplink the signal to the broadcasttransmitter 118. The broadcast transmitter 118 generates the Ntransmitter streams 1012A-1012N from the received single data streamusing splitter or demultiplexer 1010, and transmits the N transmitterstreams 1012A-1012N to the receiver station(s) 108 via transmitters1014A-1014N. Thus, only one receiver 1006A is required, and multiplexer1008 is not required.

In another possible embodiment, a plurality of uplink data streams 116are required to provide the K elementary data streams to the broadcasttransmitter 118, but only one transmitter (e.g. 1014A) is required totransmit those K elementary data streams to the receiver station(s). Inthis embodiment, M≧2 and N=1, and transmitters 1014B-1014N, receivers1016B-1016N are not required.

In yet another possible embodiment, there is more than one uplink datastream 116 (M≧2) and more than one downlink data stream 122 (N≧2), andthe number of uplink data streams 116 and downlink data streams 122 arenot equal (M≠N). In this instance, the demultiplexer 408, transmitters1004, receivers 1006, multiplexer or recombiner 1008, splitter ordemultiplexer 1010, transmitters 1014, receivers 1016 and multiplexer502 are required to transmit and recover the K elementary data streams.

In one embodiment, the broadcast transmitter 118 takes advantage of FECdecoding and encoding wherever the signal is demodulated. In which case,if the received signal is FEC encoded, it is decoded in the broadcasttransmitted, recombined as desired and FEC encoded again beforetransmission to the receiver stations 108.

FIG. 11 is a diagram illustrating another embodiment of the generalizedtransmission system 700. In this embodiment, the broadcast transmitter118 comprises a plurality of broadcast transmitter elements 119A-D (e.g.multiple satellites, multiple terrestrial transmitters, or a combinationthereof). In this embodiment, a first subset of the M uplink datasignals 702A-702M′ are transmitted to one of the broadcast transmitterelements 119A using a first subset of the uplink sub-transmitters704-704M′ and a second subset of the M uplink data signals 702M″-702Mare transmitted to another of the broadcast transmitter elements 119Busing a second subset of the uplink sub-transmitters 704M″-704M.Broadcast transmitter element 119A includes receivers 706A-706M′ toreceive the first subset of M uplink data signals 702A-702M′, and amultiplexer or recombiner 1108A that recombines the M′ data signals toproduce a single data stream. The single data stream is demulitplexed bysplitter or demultiplexer 1110A into N′ broadcast sub-transmitterstreams, which are provided to N′ broadcast sub-transmitters 714A-714N′for transmission to the receiver stations 108. Similarly, broadcasttransmitter element 119B includes receivers 706M″-706M to receive thefirst subset of M uplink data signals702M″-702M, and a multiplexer orrecombiner 1108B that recombines the M″-M+1 data signals to produce asingle data stream. The single data stream is demulitplexed by splitteror demultiplexer 1110B into N-N′+1 broadcast sub-transmitter streams,which are provided to N′+1 broadcast sub-transmitters 714N″-714N fortransmission to the plurality of receiver stations 108.

The receiving stations 108 receive the N broadcast sub-transmitterstreams and provide them to the multiplexer 502. The multiplexer 502multiplexes the N sub-transmitter streams into a single stream, which isoptionally decoded by the decoder 504 before being demultiplexed intothe K elementary streams. Thus, a first subset of the M uplink datastreams 702A-702M′ is transmitted to one broadcast transmitter element119A and these M uplink data streams are transformed in the broadcasttransmitter element 119A into N′ broadcast sub-transmitter streams thatare transmitted to the receiver stations 108. Similarly, a second subsetof the M uplink data streams 702M″-702M is transmitted to anotherbroadcast transmitter element 119B and these M uplink data streams aretransformed in the broadcast transmitter element 119B into N-N′+1broadcast sub-transmitter streams that are transmitted to the receiverstations 108. The receiver stations 108 receive the N sub-transmitterstreams, multiplex and time-align the streams from the first broadcasttransmitter element 119A and the second broadcast transmitter element119B as described above to assemble the K elementary streams.

Hardware Environment

FIG. 12 is a diagram illustrating an exemplary computer system 1200 thatcould be used to implement elements of the present invention. Thecomputer 1202 comprises a general purpose hardware processor 1204Aand/or a special purpose hardware processor 1204B (hereinafteralternatively collectively referred to as processor 1204) and a memory1206, such as random access memory (RAM). The computer 1202 may becoupled to other devices, including input/output (I/O) devices such as akeyboard 1214, a mouse device 1216 and a printer 1228.

In one embodiment, the computer 1202 operates by the general purposeprocessor 1204A performing instructions defined by the computer program1210 under control of an operating system 1208. The computer program1210 and/or the operating system 1208 may be stored in the memory 1206and may interface with the user and/or other devices to accept input andcommands and, based on such input and commands and the instructionsdefined by the computer program 1210 and operating system 1208 toprovide output and results.

Output/results may be presented on the display 1222 or provided toanother device for presentation or further processing or action. In oneembodiment, the display 1222 comprises a liquid crystal display (LCD)having a plurality of separately addressable pixels formed by liquidcrystals. Each pixel of the display 1222 changes to an opaque ortranslucent state to form a part of the image on the display in responseto the data or information generated by the processor 1204 from theapplication of the instructions of the computer program 1210 and/oroperating system 1208 to the input and commands. Other display 1222types also include picture elements that change state in order to createthe image presented on the display 1222. The image may be providedthrough a graphical user interface (GUI) module 1218A. Although the GUImodule 1218A is depicted as a separate module, the instructionsperforming the GUI functions can be resident or distributed in theoperating system 1208, the computer program 1210, or implemented withspecial purpose memory and processors.

Some or all of the operations performed by the computer 1202 accordingto the computer program 1210 instructions may be implemented in aspecial purpose processor 1204B. In this embodiment, some or all of thecomputer program 1210 instructions may be implemented via firmwareinstructions stored in a read only memory (ROM), a programmable readonly memory (PROM) or flash memory within the special purpose processor1204B or in memory 1206. The special purpose processor 1204B may also behardwired through circuit design to perform some or all of theoperations to implement the present invention. Further, the specialpurpose processor 1204B may be a hybrid processor, which includesdedicated circuitry for performing a subset of functions, and othercircuits for performing more general functions such as responding tocomputer program instructions. In one embodiment, the special purposeprocessor is an application specific integrated circuit (ASIC).

The computer 1202 may also implement a compiler 1212 which allows acomputer application program 1210 written in a programming language suchas COBOL, C++, FORTRAN, or other language to be translated intoprocessor 1204 readable code. After completion, the application orcomputer program 1210 accesses and manipulates data accepted from I/Odevices and stored in the memory 1206 of the computer 1202 using therelationships and logic that was generated using the compiler 1212.

The computer 1202 also optionally comprises an external communicationdevice such as a modem, satellite link, Ethernet card, or other devicefor accepting input from and providing output to other computers.

In one embodiment, instructions implementing the operating system 1208,the computer program 1210, and/or the compiler 1212 are tangiblyembodied in a computer-readable medium, e.g., data storage device 1220,which could include one or more fixed or removable data storage devices,such as a zip drive, floppy disc drive 1224, hard drive, CD-ROM drive,tape drive, or a flash drive. Further, the operating system 1208 and thecomputer program 1210 are composed of computer program 1210 instructionswhich, when accessed, read and executed by the computer 1202, cause thecomputer 1202 to perform the steps necessary to implement and/or use thepresent invention or to load the program of instructions into a memory206, thus creating a special purpose data structure causing the computerto operate as a specially programmed computer executing the method stepsdescribed herein. Computer program 1210 and/or operating instructionsmay also be tangibly embodied in memory 1206 and/or data communicationsdevices 1230, thereby making a computer program product or article ofmanufacture according to the invention. As such, the terms “article ofmanufacture,” “program storage device” and “computer program product” or“computer readable storage device” as used herein are intended toencompass a computer program accessible from any computer readabledevice or media.

Of course, those skilled in the art will recognize that any combinationof the above components, or any number of different components,peripherals, and other devices, may be used with the computer 1202.

Although the term “computer” is referred to herein, it is understoodthat the computer may include portable devices such as cell phones,portable MP3 players, video game consoles, notebook computers, pocketcomputers, or any other device with suitable processing, communication,and input/output capability.

Conclusion

This concludes the description of the preferred embodiments of thepresent invention. The foregoing description of the preferred embodimentof the invention has been presented for the purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise form disclosed. Many modifications andvariations are possible in light of the above teaching. It is intendedthat the scope of the invention be limited not by this detaileddescription, but rather by the claims appended hereto. The abovespecification, examples and data provide a complete description of themanufacture and use of the composition of the invention. Since manyembodiments of the invention can be made without departing from thespirit and scope of the invention, the invention resides in the claimshereinafter appended.

What is claimed is:
 1. A method for transmitting a plurality ofelementary data streams to a plurality of receivers, comprising thesteps of: generating M data streams comprising K multiplexed elementarydata streams in a first entity; wirelessly transmitting a first subsetof the M data streams to a first transmission element; wirelesslytransmitting a second subset of the M data streams to a secondtransmitter element; generating a first subset of N transmitter streamsfrom the first subset of the M data streams in the first transmitterelement by performing steps comprising: multiplexing the first subset ofthe M data streams in the first transmitter element to generate a firstsingle data stream; and demultiplexing the first single data stream intoa first subset of N transmitter streams in the first transmitterelement; generating a second subset of N transmitter streams from thesecond subset of the M data streams in the second transmitter element byperforming steps comprising: multiplexing the second subset of the Mdata streams in the second transmitter element to generate a secondsingle data stream; and demultiplexing the second single data streaminto a second subset of N transmitter streams in the second transmitterelement; transmitting each of the first subset of N transmitter streamsto the plurality of receivers using an associated one of first subset ofN broadcast sub-transmitters; transmitting each of the second subset ofN transmitter streams to the plurality of receivers using an associatedone of second subset of N broadcast sub-transmitters; wherein a firstsubset of the M data streams are wirelessly transmitted via firstcommunication path and a second subset of the M data streams arewirelessly transmitted via a second communication path spatially diversefrom the first communication path.
 2. The method of claim 1, wherein thestep of generating the M data streams comprises the steps of:statistically multiplexing the K elementary data streams into a singleintermediate data stream having a peak bit rate less than a sum of thepeak bit rates of each of the K elementary data streams; and generatingthe M data streams by demultiplexing the single intermediate datastream.
 3. The method of claim 2, wherein: the method further comprisesthe steps of: error correction encoding the single intermediate datastream; and the M data streams are generated from the error correctionencoded single intermediate data stream.
 4. The method of claim 2,wherein a bit rate of the single intermediate data stream exceeds thebit rate of any of the first set of N broadcast sub-transmitters and anyof the second set of N broadcast sub-transmitters, but does not exceedthe combined bit rate of the first set of N broadcast sub-transmittersand the second set of N broadcast sub-transmitters.
 5. The method ofclaim 2, wherein: each of the K multiplexed elementary data streams hasan associated temporally varying bit rate BRD₁(t), BRD₂(t), . . . ,BRD_(K)(t); the single intermediate data stream comprises a bit rate of${{{BRS}(t)} \geq {\sum\limits_{i = 1}^{K}\; {{BRD}_{i}(t)}}};$ eachof the first set of N broadcast sub-transmitters has an associatedmaximum bit transmission rate of BRT₁, . . . , BRT_(N′); each of thesecond set of N broadcast sub-transmitters has an associated maximum bittransmission rate of BRT_(N), . . . , BRT_(N″); and N is selected suchthat${\sum\limits_{i = 1}^{N - 1}\; {BRT}_{i}} < {{BRS}(t)} \leq {\sum\limits_{i = 1}^{N}\; {BRT}_{i}}$for all time t.
 6. The method of claim 1, wherein; the first transmitterelement comprises a first satellite; the second transmitter elementcomprises a second satellite spaced a distance from the first satellite;a first subset of the M data streams is transmitted to the firstsatellite and the second subset of the remaining M data streams aretransmitted to the second satellite.
 7. The method of claim 1, wherein;the first transmitter element comprises a first satellite; the secondtransmitter element comprises a terrestrial transmitter spaced adistance from the first satellite; a first subset of the M data streamsis transmitted to the first satellite and the second subset of theremaining M data streams are transmitted to the terrestrial transmitter.8. The method of claim 1, wherein: the first set of N broadcastsub-transmitters each use a different, non-contiguous portion of asignal spectrum; and the second set of N broadcast sub-transmitters eachuse a different, non-contiguous portion of the signal spectrum.
 9. Themethod of claim 8, wherein the different portions of the signal spectrumcomprise guard bands in the signal spectrum.
 10. The method of claim 8,wherein at least one of the first set and second set of N broadcastsub-transmitters has a different bandwidth than the other of the firstset and second set of N broadcast sub-transmitters.
 11. An apparatus fortransmitting a plurality of elementary data streams to a plurality ofreceivers, comprising: a signal distributor, for generating M datastreams comprising K multiplexed elementary data streams; a firsttransmission element, having a first set of N broadcastsub-transmitters, the first transmission element for wirelesslyreceiving a first set of the M data streams from the signal distributor,for generating a first set of N broadcast sub-transmitter data streamsfrom the received first set of M data streams, and transmitting thefirst set of N broadcast sub-transmitter data streams via an associatedone of the first set of N broadcast sub-transmitters to the plurality ofreceivers; a second transmission element, having a second set of Nbroadcast sub-transmitters, the second transmission element forwirelessly receiving a second set of the M data streams from the signaldistributor, for generating a second set of N broadcast sub-transmitterdata streams from the received second set of M data streams, andtransmitting the second set of N broadcast sub-transmitter data streamsvia an associated one of the second set of N broadcast sub-transmittersto the plurality of receivers; wherein the first transmission elementgenerates the first set of N transmitter streams from the first set of Mdata streams by multiplexing the first set of M data streams to generatea first single data stream and demultiplexing the first single datastream into the first subset of N transmitter streams; and wherein thesecond transmission element generates the second set of N transmitterstreams from the second set of M data streams by multiplexing the secondset of M data streams to generate a second single data stream anddemultiplexing the second single data stream into the second set of Ntransmitter streams.
 12. The apparatus of claim 11, wherein the signaldistributor comprises: a statistical multiplexer, for statisticallymultiplexing the K elementary data streams into a single intermediatedata stream having a peak bit rate less than a sum of the peak bit ratesof each of the K elementary data streams; and a demultiplexer forgenerating the M data streams from the single intermediate data stream.13. The apparatus of claim 12, wherein M=1 and N is an integer greaterthan or equal to two.
 14. The apparatus of claim 12, wherein N=1 and Mis an integer greater than or equal to two.
 15. The apparatus of claim12, wherein M=N and M and N are integers greater than one.
 16. Theapparatus of claim 12, wherein M≠N and M and N are integers greater thanone.
 17. The apparatus of claim 12, wherein a bit rate of the singleintermediate data stream exceeds the bit rate of any of the first set ofN broadcast sub-transmitters and any of the second set of N broadcastsub-transmitters, but does not exceed the combined bit rate of the Nbroadcast sub-transmitters and the N broadcast sub-transmitters.
 18. Theapparatus of claim 12, wherein: each of the K multiplexed elementarydata streams has an associated temporally varying bit rate BRD₁(t),BRD₂(t), . . . , BRD_(K)(t); the single intermediate data streamcomprises a bit rate of${{BRS}(t)} \geq {\sum\limits_{i = 1}^{K}\; {{BRD}_{i}(t)}}$ each ofthe first set of N broadcast sub-transmitters has an associated maximumbit transmission rate of BRT₁, . . . , BRT_(N′); each of the second setof N broadcast sub-transmitters has an associated maximum bittransmission rate of BRT₁, . . . , BRT_(N″); and N is selected such that${\sum\limits_{i = 1}^{N - 1}\; {BRT}_{i}} < {{BRS}(t)} \leq {\sum\limits_{i = 1}^{N}\; {BRT}_{i}}$for all time t.
 19. The apparatus of claim 11, wherein: the firsttransmitter element comprises a first satellite; the second transmitterelement comprises a second satellite; the first subset of the M datastreams is transmitted to the first satellite by a first subset of theplurality of uplink sub-transmitters and another subset of the secondsubset of the M data streams are transmitted to the second satellite bya second subset of the plurality of uplink subtransmitters.
 20. Theapparatus of claim 17, wherein: the first transmitter element comprisesa first satellite; the second transmitter element comprises aterrestrial transmitter spaced a distance from the first satellite; anda first subset of the M data streams is transmitted to the firstsatellite and the second subset of the remaining M data streams aretransmitted to the terrestrial transmitter.